The document discusses sex determination and sex-linked inheritance and disorders. It explains that sex is determined by the sex chromosomes contributed by the sperm and egg, with females typically providing an X chromosome and males providing either an X or Y chromosome. It describes how some traits are located on the sex chromosomes and are thus sex-linked in their inheritance. Examples of sex-linked traits and disorders are provided, such as hemophilia and color blindness, with males being at greater risk for sex-linked recessive disorders. Punnett squares and pedigrees are discussed as tools for predicting sex-linked inheritance patterns.

1. SEX DETERMINATION
• The sex of an individual is determined by
the sex chromosomes contributed to the
zygote by the sperm and the egg

2. SEX DETERMINATION
• An egg can donate an X
• A sperm can donate an X or Y
• Therefore the sperm determines the sex
of a child

3. SEX-LINKED INHERITANCE
• Some traits are
located on the
sex
chromosomes,
so the
inheritance of
these traits
depends on the
sex of the parent
carrying the trait.

4. SEX-LINKED INHERITANCE
• Most known sex-
linked traits are
X-linked (carried
on the X
chromosome).
This is probably
because the X
chromosome is
much larger than
the Y chromosome.

5. SEX-LINKED DISORDERS
• Some sex-linked traits are associated
with disorders.
• Most are found on the X chromosome,
Y-linked disorders are rare.
• Males are at a much greater risk for
inheriting sex-disorders because they
only inherit one X, so if the X has the
allele for the disorder, they will suffer
from the disorder.
• Recessive lethal X-linked traits result
in death.

6. EXAMPLES OF SEX-LINKED
TRAITS and DISORDERS
• Male pattern baldness, red-green colour
blindness, myopia, night blindness,
hemophilia

7. SEX-LINKED INHERITANCE
Punnett squares are used to
predict the outcome of sex-
linked inheritance.
Assume the trait is X-linked
unless told otherwise!
Most disorders are recessive,
some are dominant, the
question will tell you.
A “carrier” is a female who is
heterozygous for the trait.

8. EXAMPLE
• Hemophilia is a recessive X-linked
trait. What is the probability of a
couple having a hemophiliac child if
the man does not have hemophilia
and the woman is a carrier?

9. EXAMPLE

10. Sex determination
• TED Ed - Sex Determination

11. Patterns of Inheritance

12. Pedigrees
• A pedigree is a genetic
family tree that shows
how prevalent a trait is
in a family unit from
generation to
generation.
• They are often used to
track the expression of
genetic conditions and
disorders.

13. Pedigrees
• Squares represent males
and circles females.
• A coloured in shape
means that person has the
trait in question.
• A half coloured in shape
means that they are
carrying an allele for a
recessive trait.

14. Autosomal Dominant Inheritance
• Autosomal means not on the sex
chromosomes.
• Refers to those situations in which a single
copy of an allele is sufficient to cause
expression of a trait.

15. Autosomal Dominant Inheritance
• 1. Every affected person should have at least one
affected parent.
• 2. Males and females should be equally often
affected.
• 3. An affected person has at least a 50% chance
of transmitting the dominant allele to each
offspring.

16. Autosomal Dominant Inheritance
Examples
• Progeria (caused by a mutation) in which the
person ages very rapidly. They die before they can
reproduce.
• Huntington’s Disease in which the central nervous
system starts to break down around the age of 30.

17. Autosomal Recessive Inheritance
• Refers to those situations where two
recessive alleles result in a trait being
expressed.

18. Autosomal Recessive Inheritance
• 1. An affected person may not have affected parents. Parents
would be carriers.
• 2. Affects both sexes equally. Can appear to skip generations.
• 3. Two affected parents will have affected children 100% of the time.

19. Autosomal Recessive
Examples
• Albinism is a genetic condition which is the loss
of pigment in hair, skin and eyes.
• Tay Sachs is a genetic disorder which is a build
up of fatty deposits in the brain, eventually
proving to be fatal.

20. X – linked Recessive Inheritance
• Refers to those situations where a recessive
allele on the X chromosome can lead to a
trait/condition or disorder.

21. X – linked Recessive Inheritance
• Males are affected more often than females. Ratio of
8:1.
• Affected males will transmit the allele to all
daughters, but not to sons.
• Homozygous recessive females can arise only from
matings in which the father is affected and the
mother is affected or a carrier.

22. X – linked Recessive Disorders
• Hemophilia which is the inability of the blood
to clot properly.
• Duchenne Muscular Dystrophy which
causes progressive and degenerative
muscle weakness.

23. X – Linked Dominant Inheritance
• Refers to situations where a single dominant
allele on the X chromosome can lead to a
trait/condition.
• Very uncommon.

24. X – Linked Dominant Inheritance
• 1. Twice as many females are affected as males.
• 2. Usually half the children of an affected female will be
affected, regardless of sex.
• 3. All the daughters of an affected male will be affected but
none of the sons.

25. X – Linked Dominant Example
• Vitamin D resistant rickets which can
lead to bone deformities, particularly in
the lower limbs (bowed legs).

26. PEDIGREES
• Chart showing genetic relationships between members
of a family
• Squares represent males, circles females
• Colour shows infected person, ½ shaded shows carrier